Smtpd doesn't look into /mail/lib/blocked itself (anymore).  Ratfs
does that.  Smtpd looks into /mail/ratify

Reference: /n/sources/patch/applied/man-6-smtpd-ratfs
Date: Tue Jan 24 17:38:07 CET 2006

--- /sys/man/6/smtpd	Tue Jan 24 17:37:50 2006
+++ /sys/man/6/smtpd	Tue Jan 24 17:37:44 2006
@@ -206,9 +206,12 @@
 .SS Blocked Addresses
 When
 .B /mail/lib/blocked
-exists and is readable,
+exists and is readable, and if
+.IR ratfs (4)
+is running,
 .I smtpd
-reads a list of banned addresses from it.
+looks for banned addresses in
+.B /mail/ratify.
 Messages received from these addresses are
 rejected with a 5\fIxx\fP-series SMTP error code.
 There is no option
@@ -303,4 +306,5 @@
 to exposed systems.
 .SH "SEE ALSO"
 .IR mail (1),
+.IR ratfs (4),
 .IR scanmail (8)